ASTM_B_781_-_93a_2012.pdf

Designation:B78193a(Reapproved 2012)Standard Guide forSilver-Cadmium Oxide Contact Material1This standard is issued under the fixed designation B781;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This guide provides guidelines for users and manufac-turers of silver-cadmium oxide material produced in strip,rod,wire,and part form for electrical contact applications.1.2 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to become familiarwith all hazards including those identified in the appropriateMaterial Safety Data Sheet(MSDS)for this product/materialas provided by the manufacturer,to establish appropriatesafety and health practices,and determine the applicability ofregulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2B311 Test Method for Density of Powder Metallurgy(PM)Materials Containing Less Than Two Percent PorosityB476 Specification for General Requirements for WroughtPrecious Metal Electrical Contact MaterialsC914 Test Method for Bulk Density and Volume of SolidRefractories by Wax ImmersionNOTE1Test Method B311 is applicable to fully dense forms.Specification B476 is applicable to strip,rod,or wire only.Test MethodC914 is applicable to forms less than 99%dense.3.Terminology3.1 lot,n(usage involving discrete manufactured parts)all parts of the same form,and dimensions,from the same alloymelt or batch of particulate(if manufactured by consolidation),processed under the same conditions,and submitted for inspec-tion at the same time.4.Significance and Use4.1 Silver-cadmium oxide is a popular contact material thathas been used in a wide range of applications in switches,relays and contactors for switching lamps,motors and resistiveloads.Silver-cadmium oxide is a composite material consistingof a metal matrix,silver,with a metal oxide,cadmium oxide,dispersed throughout the matrix.Compositions of up to 30%cadmium are made,but most applications use silver-cadmiumoxide in the range of 10 to 15%cadmium oxide by weight.Several different processes are used for manufacturing silver-cadmium oxide material and it should be understood that themanufacturing method has an influence on the properties of thematerial such as arc erosion resistance,welding resistance,arcmobility and contact resistance.Since the performance ofcontacts in a device is dependent on numerous factors outsidethe contact itself(opening speed,closing speed,contactpressure,contact bounce and many more device parameters),the guide cannot ensure performance in specific applications.4.2 Arc erosion resistance and welding resistance are im-proved by the addition of cadmium oxide to the silver matrix.The contact resistance is raised by this addition but still is low.Cadmium oxide and silver do not alloy so the silver matrixretains its high conductivity.Silver-cadmium oxide contactsare used in current ranges of a few amperes to several hundredamperes.4.3 Silver-cadmium oxide contact material is available aswire,silver-clad wire,sheet,strip,toplay,inlay and overlaysheet or strip,discrete contact parts,brazed contact assemblies,solid and composite rivet contacts and clad contact tapes.4.4 Materials with higher cadmium oxide contents havelower material costs but may have higher processing costs dueto lower formability.5.Manufacture5.1 Since the manufacturing method has a significant influ-ence on the properties and microstructure of silver-cadmiumoxide materials,it is important to understand some basicinformation on the types of manufacturing.Silver-cadmiumoxide manufacturing can be first divided in two categories:Internal Oxidation and Power Metallurgy.5.1.1 Internal oxidation means that the cadmium oxideparticles are formed by diffusion of oxygen into the silver alloyto combine with cadmium atoms to form cadmium oxideparticles.This process can be further divided into the catego-ries of post and pre-oxidized materials.The post-oxidizedprocess consists of performing the diffusion process after the1This guide is under the jurisdiction of ASTM Committee B02 on NonferrousMetals and Alloys and is the direct responsibility of Subcommittee B02.05 onPrecious Metals and Electrical Contact Materials.Current edition approved May 1,2012.Published May 2012.Originallyapproved in 1987.Last previous edition approved in 2006 as B781 93a(2006).DOI:10.1520/B0781-93AR12.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United